1. Field of the Invention
The present invention relates to an electronic braking and energy recycling system associated with a direct current (DC) brushless motor, which can achieve a controllable inverse torsion or damping force, for motor braking by using a set of specially defined simple gate signals. Particularly, this present invention can obtain a theoretically maximum recycling proportion of a dynamic power, without the need of altering any hardware structure of the conventional system of this kind.
2. Description of the Prior Art
Earlier electronic brake systems are all developed for the electrical products requiring a constant speed control, such as medical scooter and electro-trailer used in market or factory. All these electrical machines are typically requested with a safe and reliable electronic speed-control mechanism. In this regard, how to provide such electrical products with a smooth and reliable friction in a brake task is a the key point to the electrical products themselves. An electricity-activated vehicle is expected to have good ability in continuous work provided as the promotion of the electronic and electrical technologies increase. That is because a direct current (DC) motor can be used simultaneously for converting an electrical energy into a dynamic power and converting a dynamic power into an electrical energy by a dynamoelectric mechanism. To approach this goal, the efficiency of the energy using in the vehicle becomes to be the key point in the future research. Therefore, how to make the dynamic power efficiently conversed into electrical energy, which can be then restored back to a battery, as braking the vehicle via the same DC brushless motor is apparently an essential issue for the current research and development.
A DC brush motor has the advantages of easy control, owing to the only one set of equivalent internal windings, and lower cost of a controller thereof although it has the problem of powder dust resulted from a carbon brush and a carbon brush resistance. In the recent years, the high power metal oxide semiconductor field effect transistor (MOSFET) is capable of controlling the electrical energy at a relatively higher efficiency as the development of the power electronics. Thus, the electronic braking is not solely aimed at providing the friction needed during speed decreasing of the vehicle. At this time, the electronic braking system is expected to become a subject in the field of the reliable and high efficient DC brushless motor.
However, most of the current electromechanical systems are still built with the DC brush motor, considering that the smooth and reliable speed control can be supported by the simple control criterion in the DC brush system. The way the braking system of the DC brush motor works can be referred to FIG. 1, FIG. 2 and FIG. 3. Since only a single equivalent coil exists within the DC brush motor, the direction of a torsion of the motor is determined by the direction of the electrical current flown through this single coil. The direction of the electrical current flown through the coil, i.e. the direction of the torsion of the motor, can be readily determined by the switch-on/off states of the four MOSFETs shown in FIG. 1. Since an induced voltage on the equivalent coil of the motor is approximately proportional to a rotation speed of the motor, the induced voltage of the motor is relatively larger as the vehicle braked from a high speed, and even equals to the battery voltage as under the maximum motor speed. In this mode, turning on any lower-side MOSFET will makes the induced voltage magnetizing the inductor of this equivalent coil. Moreover, as the lower-side MOSFETs are turned off, an induced electromotive force produced by the magnetized inductor will force the inertial current to flow through the body diodes of the MOSFETs, forwarding the electrical energy back to the electrical power side. When the motor is at the lower speed mode, the induced voltage on the motor coil is also relatively lower (ε_motor×Δt_ON=L_motor×Δi_motor), making the above mechanism incapable of providing a sufficient torsion for braking of the vehicle. Thus, an inverse current has to be initialized so as to obtain sufficiently inverse torsion. Therefore, such an electronic braking mechanism is a sort of wasting electronic energy to resist the motor rotation. Due to the added current with the same direction as the one of the induced electromotive force, the current flown through the windings increases very quickly and there is no sufficient releasing duty for both of the electrical energy from the power system and the induced voltage from the rotating motor. Furthermore, the increased range of the inverse torsion has to be carefully controlled and the mechanic braking system has to be suitably provided, so that the electro-activated vehicle would not move backwards during braking. In light of the above, the conventional electronic brake system does not consider the issue of energy recycling but only aims to the efficient control of the electrical machine. Thus, the conventional brush control system can only provide the braking function without appropriately saving the supplied electrical energy.
With related to the operation of the conventional DC brushless motor, it is referred to in FIG. 4. As shown, the motor has three-phase windings, which are inherently difficult to be used for electronic braking or energy recycling. The motor can be traditionally considered as an inductor on which an induced voltage presents, which reflects the rotation speed of the motor. Theoretically, it is possible to switch between the solid switch-relay or other electronic switch, such as MOSFET and BJT, so that the dynamic power can be redirected back to the battery corresponding to the induced voltage or a super capacitor. In this way, it is operated by restoring the dynamic power back to the electrical energy and controlled only based on the detected induced voltage. Thus, complexity for control can be truly reduced and the current between the phases of the motor can be theoretically exempted from being out of control and thus from burning down the whole system. However, it is not allowable for any capacity difference between cell individuals of the battery. On the other hand, in the case of the super capacitor, a boost converter is required for boosting of the DC voltage accepted at the power end. At this time, not only a conversion efficiency of the electrical energy has to be considered, but also an additional circuitry is required.
Considering applying the control mechanism of the DC brush motor onto the DC brushless motor, the control mechanism is likely to be those shown in FIG. 5 and FIG. 6. Miserably, the same problems are also encountered. For example, the different control mechanisms correspond to the induced voltages associated with high and low speeds have to be provided concurrently. In the low speed mode, the torsion increases dramatically, resulting in a low proportion of energy recycling. At this time, the braking function can only be achieved by resorting to a mechanical design. At the same time, a bi-directional current sensor has to be built to detect the magnitude of the inverse current flown through the coil. More importantly, this braking mechanism can only be effective under the situation where the other two phases of the motor does not produce any other induced current owing to the induced voltage of the subject phase and thus interfere the control mechanism as previously designed.
Therefore, there are still many problems to be overcome in the conventional technology.
In light of the above mentioned problems and shortcoming, the inventor of the present invention sets forth, after years of research effort, an electronic braking and energy recycling system associated with a DC brushless motor.